Sex differences in pain perception have been noted in multiple studies, with
women typically displaying lower pain tolerance than men, but it is unknown
whether the mechanisms underlying these differences are hormonal, genetic or
psychosocial in origin. For example, some researchers have suggested that men
are more motivated to express a tolerance for pain because masculine stereotyping
encourages it, while feminine stereotyping encourages pain expression and lower
pain tolerance.
“These findings suggest that motivation does not account for the sex
difference in pain tolerance,” says study author Roger B. Fillingim,
Ph.D., of the Department of Operative Dentistry at the University of Florida
and the Gainesville VA Medical Center in Gainesville, Fla.
Fillingim and colleagues enlisted 81 undergraduates at the University of Alabama
at Birmingham, with roughly equal numbers of males and females, as study participants.
Half of the students were assigned to a low-incentive group, in which students
received just 5 cents for every 15 seconds they kept their hand submerged in
ice water. The remaining students in a high incentive group received $1 for
every 15 seconds their hand remained submerged.
Before enduring the cold water, students were asked to predict how painful
the experience would be, how they would perform and how motivated they were
by the monetary reward. During the experience, in which they submerged their
right hand in cold water up to their wrist until they could no longer tolerate
the pain, the researchers measured their pain and took blood pressure and heart
rate measurements. After removing their hand from ice water, the students completed
questionnaires that measured their pain, stress, perceived performance, and
motivation to keep their hand submerged.
Like in previous pain studies, males had higher pain thresholds and tolerances
than females, with the female students providing higher pain ratings 30 seconds
after their hand was submerged, as well as on the questionnaire afterward.
The study results are published in the current issue of Psychosomatic
Medicine.
The researchers predicted that participants with a greater incentive to endure
the cold water would exhibit a more robust heart rate or higher blood pressure
responses, but this did not happen. Instead, blood pressure and heart rate
measures increased equally across all groups during the cold water submersion.
But the researchers did note differing patterns of responses depending on incentive.
“The monetary incentive did not influence pain responses, but the relationship
between cardiovascular measures and pain responses was influenced by the incentive
manipulation,” says Fillingim. Specifically, low incentive subjects
with higher blood pressure at the start of the study period tended to tolerate
pain
better. But this association was not seen in the high incentive subjects.
For the high incentive subjects, a leap in blood pressure (which is a sign
of being
engaged in a task) was associated with having higher pain tolerance.
The researchers point out that psychological factors can
influence the association between physiological responses — such as heart rate and blood pressure — and
pain responses. It is important to understand “these complex interactions
among biological and psychosocial variables, rather than artificially separating
their effects,” says Fillingim says.
“Additional research is needed to replicate these findings and to further
elucidate the relationships among motivation, gender roles, and pain responses,” he
concludes.
This study was supported by National Institutes of Health.
